Featured Research

from universities, journals, and other organizations

Molecular Bridge Serves As A Tether For A Cell’s Nucleus

Date:
August 13, 2008
Source:
Rockefeller University
Summary:
A cell's nucleus -- home of it its most precious contents -- is a delicate envelope that, without support, is barely able to withstand the forces that keep it in place. Now, researchers have discovered a network of molecules in the nuclear membrane that provide the nucleus with rigidity and also facilitate a previously undiscovered form of communication between the cell's nucleus and its cytoplasm.

Misshapen membrane. When cells lack the protein Ima1, their nuclei appear deformed (bottom) rather than spherical.

A cell’s nucleus — home of it its most precious contents — is a delicate envelope that, without support, is barely able to withstand the forces that keep it in place. Now, researchers have discovered a network of molecules in the nuclear membrane that provide the nucleus with rigidity and also facilitate a previously undiscovered form of communication between the cell’s nucleus and its cytoplasm.

Scientists, led by Nobel Prize winner Gόnter Blobel, say that this mechanism is different from the usual traffic of molecular signals that enter and exit the nucleus through pores in the nuclear envelope.

“This is a distinct kind of physical connection between two compartments in a cell — the cytoplasm and the nucleus,” says the study’s lead investigator, Megan King, of Blobel’s Laboratory of Cell Biology. “It really opens up the possibility that there is a basic process going on that affects gene expression in ways that we had not understood before.”

King describes the network as a bridge of molecules that extends from the interior of the nucleus — specifically, the chromatin, the complex of DNA and proteins that makes up chromosomes – into the cell cytoplasm and its network of microtubules that provides structure to the cell. Though some of the proteins had been previously identified, King, Blobel and researcher Theodore Drivas discovered one in particular, called Ima1, that serves as one of the bridge’s pillars.

In fission yeast, the single-cell eukaryotes that the researchers used as a model organism, the nucleus has to stay centered within the cell before cell division is initiated. In other eukaryotes, microtubules push on the nucleus by interacting with nuclear membrane proteins from two previously discovered families: KASH domain proteins, which span the outer nuclear membrane, and SUN domain proteins, which reside in the inner nuclear membrane. However, King and the other researchers suspected that this bridge alone could not be strong enough to keep the nuclear structure stable against the forces applied by the cell’s cytoskeleton.

The researchers now say that two additional proteins are part of the yeast nuclear bridge. One is Kms2, which is part of the KASH family, and the other is Sad1, a member of the SUN family. Kms2 forms the outside pillar of the bridge and couples forces from microtubules to the protein bridge anchored on the inside by Sad1. But the scientists suspected there had to be an anchor for Sad1, or the bridge could not withstand such forces.

They then examined Ima1, which is found in many species, including humans. The protein binds to heterochromatin, which is a tightly packed form of DNA and is critically located in the inner membrane of the nucleus. Indeed, a series of experiments demonstrated that Ima1 forms the strong ground support for the side of the bridge that attaches inside the nucleus, and that other proteins, namely the Ndc80 complex, strengthen the connection, like a nut-and-bolt arrangement. Together, they proved able to absorb the forces transmitted through the centrosome on the outside of the nucleus. Whenever Ima1 or the Ndc80 complex was compromised, the bridges fell apart.

“The proteins act like players in a game of tug-of-war,” says King. “They will move side to side in an ordered line, remaining standing as long as the teams are of similar strengths. However, once one team pulls with a force that cannot be countered by the second team, both teams fall to the ground in a jumble.” When decoupled from chromatin, the nuclear envelope pays the price, becoming deformed and fragmented.

“This communication is physical, and it shows us how chromatin can support a cytoplasmic function, while, on the other hand, microtubules have the ability to affect nuclear functions,” King says.


Story Source:

The above story is based on materials provided by Rockefeller University. Note: Materials may be edited for content and length.


Journal Reference:

  1. King et al. A Network of Nuclear Envelope Membrane Proteins Linking Centromeres to Microtubules. Cell, 2008; 134 (3): 427 DOI: 10.1016/j.cell.2008.06.022

Cite This Page:

Rockefeller University. "Molecular Bridge Serves As A Tether For A Cell’s Nucleus." ScienceDaily. ScienceDaily, 13 August 2008. <www.sciencedaily.com/releases/2008/08/080811085435.htm>.
Rockefeller University. (2008, August 13). Molecular Bridge Serves As A Tether For A Cell’s Nucleus. ScienceDaily. Retrieved July 29, 2014 from www.sciencedaily.com/releases/2008/08/080811085435.htm
Rockefeller University. "Molecular Bridge Serves As A Tether For A Cell’s Nucleus." ScienceDaily. www.sciencedaily.com/releases/2008/08/080811085435.htm (accessed July 29, 2014).

Share This




More Plants & Animals News

Tuesday, July 29, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Rodents Rampant in Gardens Around Louvre

Rodents Rampant in Gardens Around Louvre

AP (July 29, 2014) — Food scraps and other items left on the grounds by picnickers brings unwelcome visitors to the grounds of the world famous and popular Louvre Museum in Paris. (July 29) Video provided by AP
Powered by NewsLook.com
Deadly Ebola Virus Threatens West Africa

Deadly Ebola Virus Threatens West Africa

AP (July 28, 2014) — West African nations and international health organizations are working to contain the largest Ebola outbreak in history. It's one of the deadliest diseases known to man, but the CDC says it's unlikely to spread in the U.S. (July 28) Video provided by AP
Powered by NewsLook.com
Traditional African Dishes Teach Healthy Eating

Traditional African Dishes Teach Healthy Eating

AP (July 28, 2014) — Classes are being offered nationwide to encourage African Americans to learn about cooking fresh foods based on traditional African cuisine. The program is trying to combat obesity, heart disease and other ailments often linked to diet. (July 28) Video provided by AP
Powered by NewsLook.com
Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Asteroid's Timing Was 'Colossal Bad Luck' For The Dinosaurs

Newsy (July 28, 2014) — The asteroid that killed the dinosaurs struck at the worst time for them. A new study says that if it hit earlier or later, they might've survived. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins